Blade for a dry shaver



Noy. 20, 1962 J. F. WAHL 3,064,348

BLADE FOR A DRY SHVER Filed Feb. 15, 1960 FIG, l Fife. Z Z l' "mw-'nid T- 2 22 g@ @M-2' f un uzlgun l EU -:i-:TD:

3f 3 (34 John E Wahl Wkw 1@ www' Jorneys United States Patent Office 3,0b4i3 Patented Nov. 20, 1952 3,064,348 BLADE FOR A DRY SHAVER John F. Wahl, Sterling, Ill., assigner to Wahl Clipper Corporation, Steriing, Ill., a corporation of Illinois Filed Feb. l5, 1960, Ser. No. 8,790 1 t'llaim. (Cl. 30-43) This invention relates to the movable blade in a dry shaver, and this application is a continuation-in-part of my prior co-pending applications Serial Nos. 535,570 now Patent No. 2,959,854 granted November l5, 1960 and 7 55,457 now abandoned.

Dry shavers typically comprise a fixed resilient outer or shear blade and a movable vibratory inner blade. These blades cooperate with each other to cut hair in a manner well known in the art.

In the past, dry shavers utilized a movable inner blade which was substantially rigid, and in most instances this inner blade was mounted in a resilient manner. With this arrangement, the resilient outer blade could yield somewhat because of the resilient mounting of the inner blade. The disadvantage of this arrangement was that when the outer blade yields, a certain amount of bearing contact between the two blades is lost. This concentrates the bearing contact between the blades at fewer points and makes the outer blade susceptible to being broken or torn. It also adversely affects the cutting operation of the shaver.

The outer or shear blade is generally constructed of sheet metal and is thin and resilient with a perforate cutting region. If the inner blade were also formed from thin resilient sheet metal perforated over the cutting region, then when the cutting region of the fixed outer blade is deformed, the cutting region of the inner movable blade may deform to conform to the deformed shape of the outer blade. In this way the bearing contact between the fixed outer blade and the movable inner blade will be maintained over the cutting region when the fixed outer blade yields or deforms during the shaving operation.

The thickness and the form of the perforated cutting region of such an inner blade is quite critical and apparently minor changes in the shape of the perforations and the metal between the perforations may produce large changes in cutting efficiency and in the closeness and the speed of the shave.

What is needed therefore, and comprises an important object of this invention is an inner blade for a dry shaver formed from thin resilient sheet metal with a perforated cutting region which is shaped to permit the inner blade to deform to conform to deformations in the outer blade and which cooperates with the fixed outer blade in giving a close and rapid shave.

This and other objects of this invention will become more apparent when read in the light of the specification and the accompanying drawings wherein:

FIG. l is a view of the dry shaver with the cover casing and outer blade removed showing the vibratory motor and its connection to the inner movable cutting biade;

FIG. 2 is a plan view of the inner movable cutting blade;

FIG. 3 is a sectional view taken on the line 3-3 of FIG. l;

FIG. 4 is an enlarged sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a view of the inner movable cutting blade during the course of its manufacture showing the way the sharp cutting edges are formed on the blade teeth; and

EG. 6 is a plan view of the inner movable cutting blade before it is bent into its arcuately curved form.

Referring now to FIG. 1 of the drawing, a dry shaver indicated generally by the reference numeral 10 includes a vibratory electric motor 12 mounted in a casing section 14. The vibratory electric motor 12 is provided with a magnetic core 16, and an armature 18 is mounted for vibratory movement in association with the pole faces 0f the core in a manner well known in the art.

A drive iinger 20 is connected at one end to the free end of the armature 1S and at the other end to the base 22 of an arcuately cur-ved inner movable cutting blade 24, see FIG. 3. The inner movable cutting blade is formed from initially flat pre-hardened sheet metal about .0030 inch thick, and has a perforated cutting region 25, see FG. 6. The perlorations in this embodiment consist of elongated slots 26, see FIG. 2. These slots are disposed along parallel lines and the slots in each line are separated from each other by blade portions 28. The blade strips between the slots constitute teeth 30 and in this embodiment the teeth extend in a straight line perpendicular to the direction of blade movement.

The sides of the teeth 30 constitute cutting edges 32 and, as seen in FIG. 4, these edges are formed by the intersection of the outer or cutting surface 34 of blade 24 adjacent inner surface 36 of the outer blade 38 and the surface 40 of the blade metal of the teeth facing the perforations or slots 26. The intersection of surfaces 34 and 40 forms an acute angle 33 so that the cutting edges 32 are sharp. ln addition, as seenin FIG. 4, the cutting edges 32 are upturned so that only the sharp cutting edges 32 bear against inner surface 36 of the fixed outer blade 3S. This is an important feature because with just the cutting edges 32 of the teeth bearing against the inner surface 36 of the fixed outer blade, frictional resistance due to the rubbing engagement between the inner and outer blades will be reduced. This lessens power requirements and motor size resulting in a decrease in manufacturing cost.

The acute angle 33 of the intersecting surfaces of the cutting edge 32 conveniently may be formed by an acid etching process. With the cutting blade 24 in an initially flat position, as shown in FIG. 6, an acid resistant coating 42 completely covers one surface of the blade 24 and covers all parts of the opposite surface of the blade except where the slots 26 are to be formed, see FIG. 5. Then when the blade is inserted in a suitable acid bath, the acid in contact with the exposed parts of the metal will gradually eat its way through the metal in the manner indicated by the vertically spaced dotted curves in the slots 26 in FIG. 5. As the acid eats its way through the metal it. 4forms the cutting edges 32 with the desired acute angle 33.

The blade 24 is arcuately bent so at least the cutting region 25 has a continuous and uniform curvature in cross section and so the teeth 30 follow the arcuate periphery of the bent metal. Then the blade is mounted on the cutting head of the shaver as shown in FIG. 3. With this arrangement, the stress in the pre-hardened sheet metal causes the sharp cutting edges 32 to curve upwardly as shown in FIG. 4. The magnitude of the upward curve is not great, and benefits occur if the metal is stressed enough so that the cutting edges 32 are raised as little as 0.000005 inch above the cutting surface 34 of blade 24. In practice, it has been found that the edges of a properly designed blade will be raised about 0.0002 inch. The result of forming the inner movable cutting blade this way is an electric shaver which gives a close, comfortable and rapid shave.

From the above description it is thought that the construction and advantages of this invention will be readily apparent to those skilled in the art. Various changes in detail may be made without departing from the spirit or losing the advantages of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

3 1% An -inner cutter blade for a dry shaver comprising: ing outer blade, thus providing improved cutting a thin sheet of hardened metal having laterally spaced characteristic and reduced bearing surface.

elongated slots therein, the metal between adjacent 1lslots consjtitutinfg teeth;f h h 1 d References Cited in the le of this patent it e two si e sur aces o eac toot inc ine at an 5 acute angle Withthe'top tooth surface to dene acute- UNITED STATES PATENTS angle cutting edges on each tooth; 2,132,644 Rand et a1 OC- 11, '1938 said slotted sheet 'having a continuous and uniforfn 2,141,582 Wimbefgel' DeC 27, 1933 curvature With said top tooth surfaces on the outside 2,355,898 saXe Allg- 15, 1944 of the curvature; 10 'the acute-angle cutting edges of said teeth raised above FOREIGN PATENTS said tooth top surfaces'by at least 0.000005 inch and 735,382 France Aug. 23, 1932 'adapted to bear on the inside surface of a cooperaty526,677 Great Britain Sept. 24, 1940 

